In this project we focus on the inter-relationships among mechanics, adhesion, signaling, and microvascular flow. Two aims (Aims 1 and 2) represent continuing interests from the present funding period. Aim 1 is related to the consequences of abnormal erythroid mechanical function on cell survival and flow in the microvasculature. Our recent findings to date confirm the expectation that the most important determinant of red cell viability is that it have sufficient membrane area to enclose its volume within the constrains of the microvasculature. In the next period we will continue to take advantage of the unique combination of expertise in this program and extend these studies to determine the impact that abnormal erythrocyte deformability has on cell distribution and microvascular flow. The second continuing aim (Aim 2) is related to development of proper erythroid and microvascular flow. The second continuing aim (Aim 2) is related to the development of proper erythroid mechanical function during late-stage maturation. Substantial preliminary progress has been made with regard to this aim because of a new collaboration with Dr. David Wu, who is expert on advanced bone marrow culture technology. By combining packed bed cell culture techniques with micromechanical testing of immature erythroid cells, we can make important contributions to understanding how red cell precursors develop into mature functioning cells and what conditions are important for the proper development of membrane stability that is essential for red cell function. Specific Aim 3 is based on a new interest centered on the role that mechanics play in the initiation and stability of strong adhesive contacts between neutrophils and endothelium. In spite of the significant progress that has been made in studies of leukocyte-endothelial cell interactions, significant questions remain about the precise mechanisms involved in determining the specificity of interaction and regulation of the transition from rolling to arrest to diapedesis. Micromechanical manipulation of single cells provides unparalleled ability to control both the chemical environment and the mechanical forces involved in cell-cell interactions, so that the specific role that cellular mechanics plays in the formation of adhesive contacts and the generation of signaling cascade to modify and regulate cell behavior can be deduced.